CS227293B1 - Method of semi-continuous solvent polymerization or copolymerization of unsaturated monomers - Google Patents

Description

The invention relates to a semi-continuous process for preparing polymers or copolymers by solution polymerization in a solvent.

The preparation of synthetic polymeric substances by solution polymerization of monomers containing a single double bond in the presence of free radical initiators or by thermal initiation is commonly known, used and also described in the literature (eg Esser F .: Polymethacrylate, Hanser Vrlg., München 1975; Kollinski F., Merk NF: Encyclopedia of Polymer Science and Technology, Vol. 14, Interscience, New York 1964, p. 1045; Marek O., Tomka M .: Acrylic Polymers, SNTL, Prague 1964). However, the actual technological verification of the relevant processes is rarely mentioned. To some extent, a certain idea of technological equipment in a continuous process can be made according to patent literature (eg Japanese patents Nos. 51,004,289 and 53,002,589).

Although the semicontinuous process is not mentioned in the literature, it is possible to deduce from these patents the advantage that the polymerization heat can be easily removed from the reaction mixture. Other publications (eg, Belgian Pat. Nos. 845 524 and 857 104) address the problem of sticking on the reactor walls and on the stirrer during polymerization and present methods to suppress their formation. However, nowhere is there any indication of how the reactants are introduced into the reaction mixture and the resulting design of the polymerization apparatus, which has now been found to be of great importance for the preparation of solution polymers and copolymers.

The present invention is directed to a process for semi-continuous solution polymerization or copolymerization of unsaturated monomers by the action of radical initiators or thermal polymerization in the presence of solvents, and optionally modifying agents and under an inert atmosphere at or below the reflux temperature of the reaction mixture using the monomer mixture reflux; solvents. The principle of the invention is that the reactants or even auxiliary components are fed to the stirred reaction medium below the level of the reaction mixture, preferably to sites with maximum mixing intensity, preferably cooled and / or mixed with each other before entering the medium. When the polymerization is carried out at the boiling point of the reaction mixture, the reflux of the monomer / solvent mixture, which is preferably mixed with the fresh monomer feed, is also introduced below the level of the reaction mixture to sites having a minimum mixing intensity. At the end of the monomer feed into the reaction mixture, the remainder of the solvent used is fed via the same route.

The advantage of the described process lies in the immediate homogenization of the feed mixture into the reaction mixture, thereby avoiding the spraying of monomers on the reactor walls and the stirrer, and thus the formation of undesirable surface stickers. In addition, the reaction proceeds throughout the volume of the reaction mixture and not only at the surface, as is currently the case with the usual introduction of monomers to the level of the mixture in the reactor. The process of the invention also makes better use of the heat exchange surface of the reactor and generally improves the homogeneity of the polymers prepared.

For mixing the reaction mixture in the reactor, multi-stage agitators with oblique or arrow blades are optimal, but other types of stirrers, such as anchor, leaf, propeller, etc., may also be used. The component supply pipe may be cooled by a medium passing through its jacket, which is usually cooling water or an inert gas used to maintain an inert atmosphere in the reactor (especially nitrogen). If the supply line is routed outside the reactor and connected to it via a flange, it need not be cooled. Advantageously, the individual components fed to the reactor may be mixed with each other prior to discharging into the reaction mixture, which is done in a mixing section to which all feed lines are connected before entering the reactor. The feed line orifice inside the reactor must then be led below the level of the reaction mixture to locations with maximum mixing intensity. This region is located within the volume of the reaction mixture at a distance of 0.05 to 0.3 times the internal diameter of the reactor from the internal surface of the reactor and depends on the type of stirrer used. In the case of an anchor stirrer, this distance is at the lower end of the range, while using a propeller stirrer in the upper part of the range.

Example 1

Weigh 8.6 kg of n-butanol and 8.8 kg of technical xylene into a 60 L reactor. The mixture is heated to boiling, i.e., 116-120 ° C, depending on the xylene composition. At this temperature, a mixture of 7.35 kg of styrene, 8.26 kg of butyl acrylate, 2.2 kg of hydroxyethyl methacrylate and 0.6 kg of acrylic acid is added below the boiling solvents together with 0.35 kg of di-tert-butylperoxide. The reaction mixture is kept at a gentle boil, the condensate from the downstream condenser being brought back below the level of the reaction mixture via the hydraulic closure. The stirrer in the reactor is anchored and the monomer and condensate feed outlets are in the gap between the stirrer blade and the reactor wall. The monomer dosing is carried out at a rate of 2.5 kg / hr. At the end of the dosing, a solvent mixture consisting of 0.5 kg of n-butanol and 0.5 kg of technical xylene is metered through the monomer route. The reaction mixture is maintained at the boiling point for a further 4 hours. The product was then filtered through a 30 µm screen.

In this way, 10 operations were performed without the reactor having to be cleaned or replaced by a filter baffle. In conducting the polymerization at which the monomers were brought to the level of the reaction mixture, after the fifth batch, the reactor had to be cleaned both by solvent and mechanically, and after each batch the filter baffle had to be replaced. The amount of polymer losses thus obtained amounted to 0.5 to 10% by weight, based on the monomers used.

Example 2

9.9 kg of technical gasoline and 2.5 kg of toluene, 4 kg of 2-ethylhexyl acrylate, 1.5 kg of butyl methacrylate, 0.2 kg of N-isobutoxymethyl acrylamide and 0.1 kg of acrylic acid are weighed into a 60 L reactor. The mixture is heated to 65 ° C and 0.04 kg of azobisisobutyronitrile, 5.5 kg of 2-ethylhexyl acrylate, 2 kg of butyl methacrylate, 0.13 kg of N-isobutoxymethylacrylamide, and 0.04 kg of the solution are added to the reactor below the solvent level. 1 kg of acrylic acid at a rate of 1.5 kg / hr. At this feed rate, the reactor temperature is maintained at 65 ° C. After the metering was completed, the reaction mixture was heated to 80 ° C and 6.2 kg of technical gasoline was fed to the reactor with the same route as for the monomers at a rate of 2 kg / h. After this time, the reaction mixture was heated to 90 ° C and maintained for an additional 2 hours. No gel particles were collected during filtration of the product, whereas in the process when the monomer mixture was brought to the surface of the reaction mixture the gel particles formed in the reactor prevented conventional filtration.

WITH

Claims (4)

SUBJECT CLAIMS 1. A process for the semi-continuous solution polymerization or copolymerization of unsaturated monomers by free radical initiators or by thermal polymerization in the presence of solvents and optionally modifying agents and under an inert atmosphere at or below the boiling point of the reaction mixture using a monomer / solvent mixture reflux. the reactants or even auxiliary components are fed to the stirred reaction medium below the level of the reaction mixture, preferably to locations of maximum mixing intensity, preferably cooled and / or mixed with one another prior to entering the medium. vynalezu 2. The process of claim 1 wherein, in the case of the polymerization conducted at the boiling point of the reaction mixture, the reflux is returned to the reaction medium below the level of the reaction mixture to the sites with maximum mixing intensity. 3. The process according to claim 1, wherein the reflux of the monomer / solvent mixture is preferably mixed with fresh monomers fed to the reaction mixture prior to entering the reaction medium. 4. The process of claims 1 and 3 wherein after the monomer feed into the reaction mixture is complete the remainder of the amount of solvent used is fed via the same route.